LCDs are widely used in various electronic information devices, such as notebooks, personal digital assistants, video cameras, and the like. A conventional LCD employs a liquid crystal panel to display images. While the liquid crystal panel contains a layer of liquid crystal for generating images, the liquid crystal does not itself generate light. Thus, light sources such as lamps are needed to provide backlight illumination of the liquid crystal.
A conventional circuit for driving the light sources includes a plurality of feedback circuits and a controller having a feedback pin electrically coupled to all the feedback circuits. Each feedback circuit corresponds to a respective light source. In operation, each of the feedback circuits detects a driving current of the corresponding light source, and accordingly generates a feedback current. All the feedback currents are directly received by the feedback pin of the controller simultaneously. The controller further controls illumination of the light sources according to the current received by the feedback pin thereof.
However, when one of the light sources is overloaded, the driving current of the corresponding light source may exceed that of others. This may cause the corresponding feedback current to be relatively higher. Because the controller receives all the feedback currents directly, the anomaly may overwhelm other feedback currents, and become a dominant factor for the illumination controlling of the controller. That is, the controller is liable to control the illumination of all the light sources merely based on the relatively greater feedback current. Thus the reliability of the circuit for driving light sources is affected.
What is needed is to provide a circuit for driving light sources that can overcome the limitations described.